Happy Birthday, Bob Irwin!

To commemorate her younger brother turning 11-years-old on Monday, Dec. 1, proud big sister Bindi Irwin, 16, took to her Instagram page to post a sweet message to her sibling.

"Happy Birthday to my wonderful little brother. He is officially 11 years old today. He's one of my best friends and always manages to make me smile," the heartfelt post began.

bindi irwin, bob irwin birthday
Instagram/@bindisueirwin

"He is more and more like Dad every day. I love him more than words and I'm so proud of the amazing human he is becoming," she wrote, referring to her late father, Steve Irwin 'The Crocodile Hunter.'

Bindi — who recently won the 2014 Australian Geographic's Young Conservationist of the Year Award — is particularly close with Bob and her mother, Terri Irwin, 50, and often posts touching messages about her family on her social media accounts.

Related Story: Bindi Irwin Writes Heartfelt Message For Her Mother's 50th Birthday

"Dad, I miss you every day. You are my superhero and my whole world. I wish you could be here, but I will do my best to make you proud. I love you more than words. Forever and always," Bindi captioned a photo of her and Steve — who passed away at age 44 from a 2006 stingray attack — in September. ❤️

bindi, steve irwin instagram